The present invention relates generally to the manufacture of pneumatic tires and, more particularly to method and apparatus for determining variations attributable to various manufacturing processes in a tire manufacturing cell, so that these variations can be minimized.
It is known in the tire and automobile industries that vehicle ride is generally a function of a number of uniformity characteristics which may be measured for tires. One of the most significant influences on tire ride is affected by the first harmonic radial and lateral force variations of a tire. The first harmonic radial force variation is often associated with xe2x80x9cradial runoutxe2x80x9d of the tire. Radial runout is defined as a difference in the radius of the tire from its axis of rotation to the outer periphery of the tire tread around the tire and may sometimes be corrected by grinding the tread rubber about the outer circumference of the tire. Radial runout may be determined by placing the finished tire in a testing machine, such as a force variation machine (FVM), which tests the tire for radial force variation as well as number of other uniformity characteristics which may be measured for tires. For example, another uniformity characteristic test which may be performed by a FVM on the tire is a test for conicity. Conicity is defined as the tendency of a rotating tire to generate a lateral force regardless of the direction of rotation of the tire. Generally, if a measured uniformity characteristic has a magnitude which is less than a predetermined lower threshold magnitude, the tire may be shipped, for installation on a vehicle. If the uniformity characteristic exceeds a predetermined upper threshold magnitude, the tire is scrapped. If the uniformity characteristic is between the lower and upper thresholds, the tire may (or may not) be corrected, for shipment and installation on a vehicle.
A typical pneumatic tire is manufactured by assembling beads, carcass plies, reinforcing members, tread rubber and sidewall rubber on a build drum. The assembled parts are inflated to form a xe2x80x9cgreenxe2x80x9d tire. Then, the xe2x80x9cgreenxe2x80x9d tire is carried from the building machine and inserted into a mold cavity for molding and curing. Pressure and heat, applied to the tire in the mold, may permanently distort the mold cavity. These distortions will be reflected in the tires manufactured with the distorted build drum and/or mold cavity. Other distortions can be caused by manufacturing variations in the molds, how the mold is mounted on the press, and variations in squeeze forces used to close the mold halves in the press. Still other distortions can be caused by differences in the constructions.
After the tire is assembled and cured, the tire is typically tested for one or more uniformity characteristics, such as by mounting the finished tire in a FVM and then inflating the tire and spinning it. The tire rubber is next ground off within the FVM in accordance with the signals generated in response to the uniformity characteristic being tested. One uniformity characteristic test which is typically performed on a finished tire is a test for radial force variation. In the radial force variation test, the finished tire is rotated in the FVM while a test wheel is pressed against the tread of the tire. Sensors in the FVM provide data indicative of the radial force exerted by the tire at each of a plurality of circumferential positions of the tire. Radial force variation can be represented by, for example, a combination of first harmonic radial force variation through an Nth harmonic radial force variation or a composite radial force variation, the Nth harmonic is the last harmonic in a Fourier Series analysis of the composite radial force variation which is deemed acceptable to accurately define the radial force variation.
A prior art system for correcting tire uniformity without grinding is described in U.S. Pat. No. 5,365,781. Sensors detect variations in characteristic parameters of a finished tire such as radial force. The radial force variation as a function of circumferential position on the tire is presented graphically as a waveform with one of the graph axes being circumferential position and another of the graph axes being radial force variation. Based on this information, the cured tire is xe2x80x9ccorrectedxe2x80x9d by permanently deforming at least one carcass reinforcing member a predetermined amount as a function of the magnitude and location (circumferential position) of the uniformity characteristic which was measured.
Another prior art system for improving tire uniformity grinding and measuring is described in U.S. Pat. No. 4,095,374. In this patent, a lateral force related to conicity is measured while the tire is being corrected by grinding for radial force variation.
A prior art tire testing apparatus is described in U.S. Pat. No. 4,134,292. In this patent, radial and lateral force are measured simultaneously at several locations on the rotating tire, and these measurements are combined to correct for the inducted disturbance of the lateral force measurement caused by the radial force.
Another prior art system for measuring uniformity of tires is described in U.S. Pat. No. 4,171,641, wherein imbalanced forces are measured and then removed from the final forces produced by a high-speed tire to give a final readout of forces which are the true dynamic road wheel contact forces on a tire under load.
Another tire testing apparatus is described in U.S. Pat. No. 5,309,377 wherein a tire uniformity inspection machine is calibrated by applying to at least one force-measuring channel thereof a signal which simulates the application of a force which is preferably of a magnitude appropriate to simulate the largest forces expected to be encountered during actual tire testing, measuring the results, and determining an appropriate calibration factor. This patent clearly illustrates a testing machine which has sensors (transducers, strain gauges) and a signal processing network, as well as a central processing unit (CPU), a display such as a cathode ray tube (CRT) and a keyboard for interacting with the signals produced by the sensors.
Another tire testing apparatus which includes video imaging is described in U.S. Pat. No. 5,347,588. This patent generates and presents to the user a video image of a tire contact patch or footprint which may be used to analyze the tire construction, operation, noise generation and performance.
The present invention advantageously employs any of the aforementioned testing and measuring processes, which are incorporated by reference herein. It should, however, clearly be understood that the present invention is directed principally towards modifying the tire-building processes (e.g., cure, mold) themselves so as to xe2x80x9cpreventxe2x80x9d tires from failing uniformity test(s), in marked contrast to techniques of the prior art which are directed towards xe2x80x9ccorrectingxe2x80x9d (fixing) already-cured tires, or calibrating test equipment.
Prior art systems generally lack the capability of providing an operator with timely feedback about how the various processes are working, except in the case of serious process defects. Feedback is typically delayed due to long process queues and transportation delays, and the information contained in consecutive measurements of tires originating from a particular piece of equipment will be lost if it is not traced.
It is an object of the present invention to provide method and apparatus for providing an operator with feedback about the operation of various processes and equipment in a tire manufacturing cell, the method and apparatus being as defined in one or more of the appended claims and, as such, having the capability of being constructed to accomplish one or more of the following subsidiary objects.
It is another object of the present invention to provide method and apparatus for providing an operator with feedback about the operation of various processes and equipment in a tire manufacturing cell, which overcome the disadvantages and limitations of the prior art methods and devices.
It is a further object of the present invention to provide method and apparatus for graphically displaying force measurements to operators of tire building and curing machines in real time.
It is a still further object of the present invention to provide method and apparatus for correlating the angular position of force variation exceptions to the angular position of the tire producing drum or tire mold cavity.
It is a yet further object of the present invention to provide method and apparatus for providing data to the operator(s) in a sorted manner.
It is a yet further object of the present invention to provide method and apparatus for normalizing the displayed data for the influence of other parts of the process.
In accordance with the invention, a self-contained tire-manufacturing cell has linked build, cure and force-measurement equipment. Each tire is tagged (personalized), such as with a bar code, so that it can be traced through the system, including which one of a number of build drums it was built upon, which one of a number of mold cavities it was cured in, and which one of a number of force variation machines it was tested on.
Further in accordance with the invention, the system performs force measurements upon each tire after curing, and provides operators with radial force measurements shortly after a tire is produced, and displays this information in a graphical symbolic format, from which process variations can readily be adduced by the operator.
In an exemplary embodiment of the invention, the force measurements for a produced tire are presented to the operator in the form of a circular band or ring on a display (video) terminal. Different angular portions of the ring are presented in different colors, as a function of force-measurement data, each color representing a predetermined range of data (i.e., within a first range, within a second range, within a third range, etc.).
In accordance with this exemplary embodiment of the invention, display data for a number of tires is presented as a sequence of a number (e.g., eight) of concentric rings on the display terminal. Preferably, the outermost ring represents the most recently produced tire, and the innermost ring represents the least recently produced tire in the sequence of tires for which data is graphically being displayed. As a new ring is added to the outside of the display of concentric rings, illustrating data for a new tire, previous rings are shrunk and the innermost ring disappears.
In accordance with an alternate embodiment of the invention, the feedback process display could be in the visual form of stacked colored bars, rather than rings, or in other configurations that may be desired.
In accordance with the invention, the operator can use a cursor to select a given one of the number of displayed rings or bars to display detailed data for the tire in numeric form. This display can also show captured process information from the other machines in the process of building that tire.